Concrete volume calculator (slab, floor, foundation)
Work out how many cubic meters of concrete your slab or footing needs. Example: a 5 × 4 m slab 10 cm thick takes 2 m³.
For ready-mix, round up when ordering (delivered per m³). For bagged concrete, check the yield on the package.
How the calculation works
The volume is length × width × thickness, with thickness in meters (cm ÷ 100). Add a waste margin (≈5%) for spillage and variation.
Examples
- A 5 × 4 m slab at 10 cm: 5 × 4 × 0.10 = 2 m³ (+ waste ≈ 2.1 m³).
- A 0.2 × 0.4 m beam, 6 m long: 0.48 m³.
Frequently asked questions
How many cement bags per m³?
It depends on the mix, but common concrete uses about 7 bags of 50 kg per m³.
Thickness in cm or meters?
Everything in meters: a 10 cm slab is 0.10 m. Mixing cm and meters gives a 10× error.
Is ready-mix concrete worth it?
For larger volumes (~3–4 m³+), ready-mix usually pays off in time and consistency. Small volumes can be mixed on site.
How many cement bags per m³ of concrete?
In a common 1:2:3 mix, roughly 350 kg — seven 50 kg bags — per cubic meter, plus about 0.7 m³ of sand, 0.8 m³ of gravel and 180 litres of water.
How much waste margin should I add?
About 5% on a well-run site and up to 10% on small jobs with improvised formwork. Running out mid-pour is far worse than having leftovers — a cold joint compromises the element.
Ready-mix or mixed on site?
Ready-mix arrives with lab-controlled strength but usually has a minimum delivery volume. On-site mixing is flexible but its strength depends entirely on site control.
Can I use this to size a slab?
No. It estimates volume for purchasing. Thickness, strength (fck) and reinforcement of any structural element must be specified by a qualified engineer.
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Updated on June 18, 2026 · by Rafael Rossi · Methodology & sources